1. Field of the Invention
The present invention relates to electronic ballasts for fluorescent and other gas discharge lamps.
2. Description of Prior Art
In power-line-operated electronic ballasts for gas discharge lamps, it is often important that the current drawn from the power line be drawn with higher power factor and lower harmonic distortion than what usually results with such power supplies.
For instance, without any added power factor correction means, the power factor associated with ordinary power-line-operated electronic fluorescent lamp ballasts will be on the order of 60% or less and the total harmonic distortion of the current drawn from the power line will be over 40%. On the other hand, in the most common of all applications of such ballasts, it is important that the power factor be at least 90% and the total harmonic distortion be no higher than about 20%.
The conventional way of improving or correcting the power factor of an inverter-type power supply involves the use of an energy-storing inductor means placed on the power-input-side of the inverter-type power supply, either just in front of or just behind the line voltage rectifier means.
One particular power factor correction circuit based on this principle is described in U.S. Pat. No. 4,075,476 entitled Sinusoidal Wave Oscillator Ballast Circuit; another one is described in U.S. Pat. No. 4,277,726 entitled Solid-State Ballast for Rapid-Start Type Fluorescent Lamps.
However, there are significant penalties in cost, weight, size and/or efficiency associated with the use of this method of power factor correction. In the present invention, electronic means effect the desired power factor correction and harmonic distortion reduction, thereby obviating the need for said energy-storing inductor, thus greatly minimizing said penalties of cost, weight, size and efficiency.